1. Field of the Invention
The present invention relates to a process for producing aldehydes by hydroformylation of a mono-olefinic compound.
2. Discussion of Background
A process which comprises reacting an olefinic compound with water gas in the presence of a catalyst to produce aldehydes or alcohols as their hydrogenated products, is well-known as a hydroformylation process. As a catalyst for the hydroformylation reaction, it is common to use a soluble complex of Group VIII metal and an organic phosphorous compound as a ligand. In general, the ligand used together with the metal component of the catalyst gives a substantial influence to the catalytic reaction. Also in the hydroformylation reaction, it is well known that the catalytic activity and the selectivity are substantially influenced by the ligand. On the other hand, in order to carry out the hydroformylation reaction industrially advantageously, it is required not only to improve the catalytic activity and selectivity but also to maintain the ligand to be stable so as not to let a decomposition reaction of the ligand including a modification reaction such as a structural change take place during the entire process for the production of aldehydes. Accordingly, various efforts to design the ligand have been made for these purposes.
Various phosphite compounds are known as a group of phosphorus compounds which may be used as the ligands for the hydroformylation reaction. In addition to simple monophosphites such as trialkyl phosphites or triarylphosphites, various phosphite compounds such as polyphosphites having a plurality of coordinating phosphorus atoms in their molecules, have been proposed. For example, JP-A-62-116587 or JP-A-6-166694 discloses a hydroformylation reaction using a bisphosphite compound wherein one of the two phosphite groups has a cyclic structure, and JP-A-62-116535, JP-A-2-231497, JP-A-6-199728 or JP-A-6-199729 discloses a hydroformylation reaction employing a bisphosphite compound wherein both of the two phosphite groups have cyclic structures. In the bisphosphite compounds used in these prior art references, 6,6'-positions of the bisarylene group as the crosslinking moiety have no substituents.
JP-A-6-184036 discloses a method for producing 1,6-hexanedials by a hydroformylation reaction of a diene such as butadiene by using a bisphosphite wherein the 6,6'-positions of the bisarylene group as the crosslinking moiety have substituents, and both of the two phosphite groups have cyclic structures. However, nothing is disclosed with respect to the function of such a bisphosphite in the hydroformylation reaction of a mono-olefin, and there is no disclosure of the stability of the bisphosphite compound.
Thus, various phosphite compounds have been proposed as ligands to be used for the hydroformylation reaction, but none of them is fully satisfactory with respect to the stability or the reactivity for the hydroformylation reaction of a mono-olefinic compound.
As described above, heretofore, various bisphosphite compounds have been proposed as ligands to be used for the hydroformylation reaction, and in the hydroformylation reaction employing such compounds, it is possible to obtain characteristic results of the reaction depending upon the structures of the bisphosphite compounds. However, it has been impossible to simultaneously satisfy a high reaction rate and a high stability of the ligands and the economical efficiency tends to be poor in a commercial production. Therefore, there has been a problem that they can hardly be used as catalysts for industrial purposes. Accordingly, it has been desired to develop a bisphosphite ligand which has excellent stability of the ligand not only in the hydroformylation reaction zone but also in the entire process, while maintaining a high reaction rate.